The Tag:SSPB entry in FlyBase represents the adaptor protein encoded by the Escherichia coli sspB gene (ECOGENE:EG10978). This protein binds specifically to the protein encoded by the Escherichia coli ssrA gene (ECOGENE:EG30100). Tag:SSPB can be used in combination with Tag:iLID to bring together two tagged proteins of interest in vivo in a light-dependent manner, for example to reconstitute a functional protein by bringing together complementary split system components, or to target a protein of interest to a particular subcellular location. The binding of Tag:iLID to Tag:SSPB is light-regulated because in the dark, binding of the SsrA sequence in Tag:iLID to Tag:SSPB is sterically inhibited, while upon blue light irradiation, a conformational change in Tag:iLID allows it to bind to Tag:SSPB. Tag:iLID increases its affinity for SspB by over 50-fold upon light stimulation (PMID:25535392).